A semiconductor exposure mask is fabricated by forming, by, for example, etching, a desired pattern on a blank mask prepared by depositing a light-shielding film (or reflecting film and a absorption film) on a glass substrate. In this case, when extraneous materials and the like exist on the glass substrate and the respective films or in the films, a light-shielding performance of the light-shielding film or a reflecting performance of a reflecting multi-layered film deteriorates. Furthermore, such materials disturb subsequent development and etching processes, and a formed pattern has an abnormal shape, resulting in risk of a mask performance drop. Therefore, at the time of fabrication of the exposure mask, whether or not extraneous materials, phase defects, and the like exist has to be inspected in a state of the blank mask.
In an exposure mask using extreme-ultraviolet rays, two different layers having different refractive index, which are called a multi-layered film, are alternately stacked as a reflecting film, so as to adjust phases of reflected light from the respective layers, thus increasing a reflectance. For this reason, when there are extraneous materials and scratches on a glass substrate, the multi-layered film formed on that substrate is locally raised or caved. In this case, since a gradient region where the phases of the reflected light are disturbed (phase defects) is generated, this region is unwantedly transferred onto a wafer at the time of exposure. Hence, as a defect inspection method of an exposure blank mask of extreme-ultraviolet rays, a method of detecting a dark-field image, and detecting signals having intensities greater than or equal to a detection threshold, which is set in advance, as defects is promising.
However, in the mask defect inspection method using a dark-field image, when a CCD camera which captures the dark-field image suffers detection noise, the detection noise is observed as a signal similar to a defect signal (false detection). Therefore, when a low detection threshold is set, it becomes easy to detect weak defect signals, but false detections tend to occur. When the false detections have occurred, operations for accessing a detection position again after inspection, and confirming whether or not a detected defect is an actual or false detection are required, thus requiring much labor and time for the inspection process. On the other hand, when a high detection threshold is set, although false detections are not easily generated, weak defect signals cannot be detected, resulting in low detection sensitivity. As a result, defects to be normally detected may be overlooked.